The present invention relates generally to feedback control systems and devices wherein a signal is created in response to certain conditions and criteria and used to control or influence external devices or systems. More specifically the present invention relates to the use of a mechanical air-fuel control to form an electrical switch to control external devices, such as an exhaust gas recirculation (EGR) system.
The present inventors are aware of various studies which have been conducted regarding EGR and its desirability during various engine operating conditions. Preliminary results of such EGR studies being conducted on the B Series diesel engines of Cummins Engine Company, Inc. of Columbus, Ind. indicate that it would be desirable to shut off EGR during air limited operation. During air limited operation (acceleration modes in Federal Transient Emissions cycle) EGR increases particulate emissions more than in any other engine operating mode. The present invention provides a mechanical air-fuel control which can be used to provide an ON/OFF signal which corresponds directly to air limited/non-air limited engine operation.
Use of the present invention is not limited to EGR and air limited operation. In a hybrid boosting system where both a turbocharger and a mechanically driven supercharger are present, the same ON/OFF signal created by the mechanical air-fuel control can be used to engage or disengage the mechanically driven supercharger. The value of this application for the present invention is to provide extra boost above that provided by the turbocharger, but only when extra boost is needed. In this way, by only engaging the supercharger when it is needed for extra boost, the fuel consumption penalty caused by use of a supercharger is reduced, and hopefully minimized.
The present inventors are aware of certain diesel engine arrangements which are equipped with both an exhaust driven turbocharger and a mechanically driven supercharger. What is believed to be a representative sampling of such diesel engine arrangements is provided by the follow patent references:
______________________________________ Patent No. Patentee Issue Date ______________________________________ 4,738,110 Tateno Apr. 19, 1988 4,903,488 Shibata Feb. 27, 1990 5,133,188 Okada Jul. 28, 1992 ______________________________________
Each of these listed patent references discloses a control system for controlling the flow of intake air and exhaust gas through the engine by both controlling the flow valves and by engaging/disengaging the mechanically driven supercharger in response to the position of an accelerator pedal or throttle. However, in each of these systems, an electrical system is used to detect the degree of depression of the accelerator pedal or throttle and to produce a corresponding output voltage. Therefore, none of these references disclose the specifics of the present invention which involves the use of a mechanical governor to create an electrical signal upon contact between a rack finger and a fuel limiting stop in order to control an EGR valve or the operation of a supercharger. Also, none of these listed patent references recognize the concept of electrically isolating a fuel limiting stop from the remainder of the engine in such a manner so as to provide contact between the moveable rack finger and the fuel limiting stop only during certain operating conditions of the engine, such as air limited operation.